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JC 9m 



Bureau of Mines Information Circular/1986 



Dust Controls To Improve Quality 
of Longwall Intake Air 



By John A. Organ iscak, Robert A. Jankowski, 
and Jonathan S. Kelly 



UNITED STATES DEPARTMENT OF THE HMTERIOR 



V 
Information Circular 9114 



Dust Controls To Improve Quality 
of Long wall Intake Air 



By John A. Organiscak, Robert A. Jankowski, 
and Jonathan S. Kelly 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



t\6- VII 



Library of Congress Cataloging in Publication Data: 




Organiscak, John A 

Dust controls to improve quality of longwall intake air. 

(Bureau of Mines information circular ; 9114) 

Bibliography: p. 8. 

Supt. of Docs, no.: I 28.27: 9114 

1. Coal mines and mining-Dust control. 2. Longwall mining. 3. Mine ventilation. 
I. Jankowski, Robert A. II. Kelly, Jonathan S. III. Title. IV. Series: Information circular 
(United States. Bureau of Mines) ; 9114. 



TN295.U4 



[TN312] 



622 s 



[622'.334] 



86-600261 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Homotropal ventilation 2 

Types of outby dust sources and controls 3 

Stageloader-crusher 3 

Panel belt 5 

Intake roadway 7 

Summary 7 

References 8 

ILLUSTRATIONS 

1. Typical homotropal ventilation of a longwall face 2 

2. Typical intake dust concentrations for antitropal and homotropal ventila- 

tion systems 3 

3. Ventilation curtain to keep headgate operator in clean air when headgate 

is restricted 3 

4. Enclosed stageloader-crusher with strategic location of water sprays 4 

5. Enclosed stageloader-crusher with a water-powered scrubber 5 

6. Panel belt dust contamination at a two-entry longwall system 6 

7. Rotary wire brush cleans conveying side of belt 7 

8. Water spray and belt wiper clean nonconveying side of belt 7 

TABLE 

1. Dust concentrations and reductions for stageloader-crusher dust controls.... 4 





UNIT OF MEASURE ABBREVIATIONS USED 


IN THIS REPORT 


cfm 


cubic foot per minute 


mg/m 3 


milligram per cubic meter 


f pm 


foot per minute 


pet 


percent 


gpm 


gallon per minute 


psi 


pound per square inch 


gal/st 


gallon per short ton 


wt pet 


weight percent 



f 



DUST CONTROLS TO IMPROVE QUALITY 
OF LONGWALL INTAKE AIR 



By John A. Organiscak, 1 Robert A. Jankowski, 2 and Jonathan S. Kelly 3 



ABSTRACT 

The Bureau of Mines has recently completed a program to identify and 
evaluate various methods that address control of dust generated outby 
the longwall mining face. Dust generated by the stageloader-crusher, 
the panel belt, and the intake roadway can be long-term throughout the 
shift, contributing significantly to the dust exposure of all face 
workers. Dust control techniques were identified and tested at a number 
of longwall mining sections located in diverse geological conditions 
across the United States. Dust controls investigated include (1) meth- 
ods that eliminate the sources of intake dust contamination — homotropal 
ventilation; (2) methods to limit the amount of respirable dust released 
into the intake airstream — improved water application and the use of 
curtains and enclosures; and (3) methods to clean the contaminated air 
prior to delivery to the mining face — scrubber systems. Usually they 
can be implemented at a low cost and can be very effective. This report 
describes each technique and its application and presents the resulting 
conclusions. 



'Mining engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 

Supervisory physical scientist, Pittsburqh Research Center. 

3 Project engineer, Foster-Miller, Inc., 350 Second Avenue, Walthan, MA. 



INTRODUCTION 



Many longwall mine operations are still 
experiencing difficulty maintaining con- 
sistent compliance with mandatory Federal 
dust standards that limit the personal 
dust exposure of longwall face workers. 
The predominant dust source is usually 
the shearer; however, several dust 
sources outby the mining face can also 
contribute significantly to personal ex- 
posure levels. Past surveys by the Bu- 
reau (1_)4 have shown that on a specific 
operation as much as 75 pet of the 
shearer operators' dust exposure came 
from contaminated intake air, while in 
many instances, approximately 25 pet of 
face workers' respirable dust exposure 
was generated outby the mining face. 



This study showed that these sources in- 
cluded the stageloader-crusher, panel 
belt, and intake roadway, with the 
stageloader-crusher being the most common 
and significant source. 

Outby dust sources can contribute sig- 
nificantly to worker dust exposure at a 
longwall face. Dust levels generated by 
these sources can be long-term throughout 
the shift and can affect all face 
workers. This report presents the ef- 
fects of homotropal ventilation, water 
application, and equipment design for re- 
ducing outby generated dust. Usually, 
these dust controls can be implemented at 
a low cost and can be very effective. 



HOMOTROPAL VENTILATION 



The most effective method for con- 
trolling intake dust is homotropal venti- 
lation, which routes air in the direction 
of coal transport along the face; i.e. , 
tailgate-to-headgate (fig. 1). This 
places the outby dust sources downstream 
of the face workers, eliminating their 
dust exposure from these sources. Intake 
dust levels are reduced in the walkway by 
as much as 90 pet (fig. 2) GO. More- 
over, the tailgate-to-headgate cutting 
cycle used in homotropal ventilation can 
increase productivity, since most of the 
coal does not have to pass through the 
shearer underframe. 

Homotropal ventilation has the drawback 
that the headgate operator works down- 
stream of the mining activities (shearer 
or plow), and tailgate entries must be 
kept in good condition. The headgate 
operator's dust exposure can be prevented 
by an auxiliary intake air split brought 
up the headgate entry next to the belt 
entry, with at least 100 fpm of airflow 
directed over the headgate operator (fig. 
1). The gob at the headgate must remain 
open so that the dust-laden face air and 
the clean auxiliary air combine at the 
headgate end of the face and flow through 

^Underlined numbers in parentheses 
refer to items in the list of references 
at the end of this report. 



the corner of the gob into the return or 
directly into the return crosscut. This 
may require additional cribbing in the 
crosscut, and between the last headgate 
shield and pillar. It is also recom- 
mended that the headgate operator con- 
trols be located as far outby the face 




< Return air 
Stopping 
I Curtain 
i — b — i Belt 
ii i ' iiii Stageloader 

FIGURE 1.— Typical homotropal ventilation of a longwall 
face. 



< 



E 
E 



rr 



UJ 



o 
o 



CO 
Q 



d.UU 




1 
KEY 


i 


1 
• 




1.60 


- •- 


- Headgate to 


tailgate 




- 




■ - 


- Tailgate to 


neadgate 






1.20 


- 


• • 


• 


• 


- 


0.80 




• m 


• 
• 


• • 


- 


0.40 










_ 






__■ f 

■ m~~ 

i 


■ 
l 


■ 





I 

Curtain 



20 40 60 

FACE LOCATION, support number 



80 



FIGURE 2.— Typical intake dust concentrations for anti- 
tropal and homotropal ventilation systems. 



as practical. This helps to keep the 
operator clear of contaminated air if the 
headgate gob should be closed up or seri- 
ously restricted, thus temporarily forc- 
ing the face air through the headgate to 
the return. A brattice curtain may have 
to be installed to insure clean intake 
air over the headgate operator when the 
face air is directed through the headgate 
to the return (fig. 3). 

On homotropal ventilated faces, the 
tailgate entries must be kept in good 
condition. Intake air travels up these 
entries, which are under additional roof 
loading from the adjacent mined-out 
panel. Some additional cribbing may be 
required, but this should not be regarded 




FIGURE 3.— Ventilation curtain to keep headgate operator 
in clean air when headgate gob is restricted. 



as an additional task, since both head- 
gate and tailgate entries are considered 
escapeways and must remain passable ac- 
cording to Federal regulations. 



TYPES OF 0UTBY DUST SOURCES AND CONTROLS 



STAGELOADER-CRUSHER 

Although homotropal ventilation is the 
most effective dust control method for 
all outby dust sources, it can be diffi- 
cult and expensive to implement. Many 
other dust source controls can be imple- 
mented at a lower cost and be very ef- 
fective in reducing outby generated dust. 



The stageloader-crusher is usually the 
most significant outby dust source on 
most longwalls. At several longwalls 
surveyed by the Bureau, more than 50 
pet of the shearer operators' dust expo- 
sure came from the stageloader-crusher 
( 1_) . Significant dust reduction can 
be achieved with water sprays lo- 
cated strategically on an enclosed 



manufacturers ' 

not enclosed, 
in the crusher 



stageloader-crusher, or with a water- 
powered scrubber that cleans the air 
inside it (3). 

Enclosing a stageloader-crusher and 
locating water sprays for optimum dust 
knockdown was evaluated at an underground 
longwall where a stageloader-crusher gen- 
erated a significant amount of respirable 
dust. Four different dust control sys- 
tems (3) were investigated as follows: 

1. Baseline condition, stageloader- 
crusher not enclosed and four hollow cone 
sprays in the crusher (waterflow, 10 
gpm). This is typical 
dust controls. 

2. Stageloader-crusher 
four hollow cone sprays 
(waterflow, 10 gpm), spray bar with two 
hollow cone sprays directed at the intake 
of the crusher (waterflow, 2 gpm), spray 
bar with three hollow cone sprays di- 
rected down on the chain conveyor on the 
discharge side of the crusher (waterflow, 
5 gpm), and a spray bar with three hollow 
cone sprays directed on and with coal 
movement on the conveyor belt immediately 
after the stageloader dump point (water- 
flow, 3 gpm). Total system waterflow was 
20 gpm. 

3. Enclosed stageloader-crusher (brat- 
tice enclosure) with only crusher sprays 
operating (10 gpm total waterflow). 

4. Enclosed stageloader-crusher (brat- 
tice enclosure) with all sprays operating 
(20 gpm total waterflow (fig. 4)). 

As can be seen from table 1, the over- 
all highest dust concentration occurred 
with the baseline dust control system: 



TABLE 1. - Dust concentrations and 
reductions for stageloader-crusher 
dust controls 



Conveyor belt 



Crusher 
sprays 

Brattice hood 




Control system 



Av dust cone, RAM units: 

Belt entry 

Stageloader 

Headgate operator 

Support 20 2 

Reduction in dust cone, 
pet: 

Belt entry 

Stageloader 

Headgate operator 

Support 20 2 



1 



1.2 
2.7 
2.4 
1.7 



BL 
BL 
BL 
BL 



0.9 
2.4 
1.0 
1.4 



25 
11 
58 
18 



1.5 
2.8 
0.9 
1.3 



-25 
-4 
63 
24 



1.0 
0.7 
0.5 
1.0 



17 
74 
79 
41 



FIGURE 4.— Enclosed stageloader-crusher with strategic 
location of water sprays. 



BL Baseline. 

'As defined in Stageloader-Crusher sec- 
tion of text: 

1 — Stageloader-crusher open, crusher 

sprays only. 
2 — Stageloader-crusher open, all 

sprays. 
3 — Stageloader-crusher enclosed, 

crusher sprays only. 
4 — Stageloader-crusher enclosed, all 
sprays. 
2 This face location chosen for compari- 
son because the airflow had ample face 
distance to stabilize from a directional 
change. 

An open stageloader-crusher with crusher 
sprays, representing a typical manufac- 
turers' dust control system. The overall 
lowest dust concentration occurred for 
the enclosed stageloader-crusher with all 
the water sprays operating. The combina- 
tion of additional water sprays and 
enclosing the stageloader-crusher reduced 
dust concentrations considerably at the 
headgate operator (79 pet), stageloader 
(74 pet), and at support 20 (41 pet); 
modest dust reductions were observed in 
the belt entry (17 pet). 

In further limited testing of the en- 
closed stageloader-crusher with addi- 
tional water sprays, the waterflow was 
increased from 20 gpm to 30 gpm, with 
most of the additional water applied 
through the crusher-sprays. A 30-pct 
additional improvement in dust levels 
was achieved at the headgate operator's 



** 



position and at support 20. No addi- 
tional improvement was recorded at the 
belt entry, indicating that the belt 
spray bar was responsible for most of the 
panel belt dust reduction. 

With all the sprays turned off, regard- 
less of whether the stageloader-crusher 
was open or enclosed, conditions deterio- 
rated, particularly in the belt entry, 
with a 100-pct increase in dust concen- 
tration at support 20. 

An enclosed stageloader-crusher with 
additional water sprays placed in stra- 
tegic locations is one of the most cost 
effective headgate dust control systems. 
The materials and labor-hours needed to 
build and maintain the system are minus- 
cule compared with the benefits gained. 

Another means of control is a water- 
powered scrubber (4^ (Jet Spray Air 
Mover, JSAM) that cleans the air inside 
an enclosed stageloader-crusher and dis- 
charges the clean air into the mine en- 
vironment (fig. 5). In this case, the 
stageloader-crusher is enclosed, but with 
an opening or ducting for the scrubber 
intake located as close as practical to 
the crusher discharge. Water sprays 
should again be added under the brattice 
hood on the intake side of the crusher, 
to knock down or contain the dust gener- 
ated by the crusher and prevent it from 
boiling out of the crusher intake. The 
scrubber should be installed on the 
stageloader to draw the air from the duct 
or opening on the discharge side of the 
crusher. The scrubber exhaust should 
discharge air in the direction of coal 
movement. 

This type of system was tested at an 
underground coal mine where the scrubber 
was supplied with approximately 9 gpm 



Water-powered 
scrubber 





Crusher intake f 
(with brattice hood 
and water spray) I — r 

Crusher 

FIGURE 5.— Enclosed stageloader-crusher with a water- 
powered scrubber. 



water at 500 psi for an airflow of ap- 
proximately 2,000 cfm through the unit. 
With all controls operating, dust re- 
ductions of approximately 75 pet were ob- 
served at the headgate operator's 
position, with a 50-pct reduction in in- 
take dust along the longwall face. The 
water pressure should be maintained at 
~500 psi for most effective results. 

PANEL BELT 

For three- and four-entry longwall 
systems, there should be no dust contami- 
nation at the face from the longwall 
panel belt, unless immense quantities of 
ventilation air are needed for methane 
control. The belt entry at most of these 
systems should be on a neutral split of 
air with perceptible airflow directed 
away from the face, and into the air re- 
turn. A properly isolated and regulated 
belt entry with a check curtain just 
outby the stageloader can provide this 
neutral split. 

It is not unusual to find longwalls 
with an inadequately regulated belt entry 
and a poorly maintained or nonexistent 
check curtain where the belt entry air- 
flow is towards the face, contaminating 
the intake air. On some two-entry long- 
walls, where a portion of the intake air 
is brought up the belt entry to ventilate 
the face (under an MSHA variance), dust 
contamination can be significant. 

The significance of belt panel dust 
contamination of the intake air to the 
face can be shown by some data from a Bu- 
reau study of stageloader-crusher dust 
controls ( 3) ■ The longwall was a two- 
entry system and brought 20 pet of its 
intake air up the belt entry. Figure 6 
shows the longwall headgate area includ- 
ing measured dust concentrations and air 
quantities. As a result of panel belt 
dust contamination (2.4 mg/m 3 in 13,500 
cfm air) , the face intake dust concen- 
tration was 0.5 mg/m 3 , based on intake 
air dilution [(13,500 cfm/70,000 cfm) 
x 2.4 mg/m 3 ] . 

Although the stageloader-crusher was 
the dominant dust source, the 0.5 mg/m 3 
dust from the panel belt is significant 
because it is usually constant throughout 



(Dust cone at support 20 
= 1.6 mg/m 3 ) 




( Dust cone = 0.3 mg/m 3 ) 



FIGURE 6.— Panel belt dust contamination at a two-entry 
longwall system. 



the shift and represents 25 pet of the 
Federal compliance limit. If the belt 
entry could be isolated and the belt 
entry air could be routed into a return, 
the panel belt contamination of the face 
intake air would be eliminated. When the 
belt entry air is needed at the face or a 
neutral belt entry is hard to maintain, 
panel belt dust controls are required. 
Even if a neutral belt entry can be 
maintained, panel belt dust should be 
controlled to keep float dust to a mini- 
mum and reduce the panel belt workers ' 
dust exposure. 

To prevent the fine dust particles from 
becoming airborne during transport, the 
coal should be wetted initially at the 
face by drum sprays (shearer face) or by 
sequential face sprays (plow face). A 
useful guide for water application is 
2 to 4 wt pet (4.5 to 9.5 gal/st) (_5). 
Water should be sufficient to wet the 
coal, but should not accumulate on the 
floor. A Bureau study (6) of double-drum 
shearers showed significant reductions 
in shearer-generated dust, in addition 
to a 25-pct reduction in the face intake 
dust at support 8, when the total water 
applied to the coal, through the drums, 
was increased from 34 gpm to 48 gpm. The 
reduction in dust generated by the outby 
sources, stageloader-crusher and panel 
belt, could not clearly be established 



but the increase in water application was 
felt to have had a positive effect on 
both crushing and transport. 

During outby transport, the water on 
the coal may evaporate, making rewetting 
necessary at intervals along the belt. 
This is accomplished by spraying water 
onto the coal, far enough inby the trans- 
fer point to allow the coal and water to 
mix, applying between 1 and 4 gpm water 
at operating pressures of 50 psi or more 
(7_). Flat fan sprays and full-cone noz- 
zles are typically used for coal wetting 
underground. 

Rewetting of the coal can reduce the 
amount of dust generated during trans- 
port. In the above two-entry panel belt 
dust contamination case, belt entry dust 
concentration was reduced by 83 pet when 
the coal was rewetted at the stageloader 
(3). A spray bar with three hollow cone 
sprays installed in an enclosed stage- 
loader downstream of the crusher, knocked 
down the dust in the stageloader and re- 
wetted the coal, thus significantly 
reducing panel belt dust generation. 

Belt maintenance and belt cleaning also 
control panel belt dust. Missing rol- 
lers, belt slippage, and worn belts can 
cause belt misalignment and create spil- 
lage that gets pulverized by the drive 
pulley on the nonconveying side of the 
returning belt. The top and bottom of 
the return belt should be cleaned 
with spring-loaded or counter-weighted 
scrapers, to prevent material adhering to 
the return belt from being pulverized by 
the tail-end pulley. A low-quantity 
water spray can also be used to moisten 
the belt slightly. Other means of clean- 
ing the return belt are a motor-driven 
rotary wire brush that cleans the convey- 
ing side by rotating opposite belt travel 
(fig. 7), and a full-cone water spray, 
directed at the nonconveying side, fol- 
lowed by a piece of carpeting (belt 
wiper) positioned across the belt width 
(fig. 8). The water spray wets the fines 
and the carpeting removes them from the 
nonconveying side. This system yielded 
more than a 90-pct reduction of airborne 
respirable and float dust, compared with 
a dry operation (8). 



Conveyor belt 




FIGURE 7.— Rotary wire brush cleans conveying side of belt. 



INTAKE ROADWAY 

Respirable dust concentrations in the 
intake air at the last open crosscut are 
usually very low, with no significant ef- 
fect on face personnel. On a typical 
longwall, background respirable dust con- 
centrations in the intake air are usually 
less than 0.3 mg/m- 5 . However, if the 
dust concentration in the intake is 
higher, it will contribute significantly 
to the dust exposure of face personnel. 

Measures to control dust sources up- 
stream of the last open crosscut can 
be as simple as limiting construction, 
haulage of supplies, and roadway grading 




FIGURE 8.— Water spray and belt wiper clean nonconveying 
side of belt. 



in the intake air during the production 
shift. If haulage activities must take 
place during a production shift, the 
moisture content of the dust on the haul- 
ageway floor should be about 10 pet to 
insure that it remains bound (J)* Plain 
water dries out rapidly in the venti- 
lation air, making repeated applications 
necessary. Addition of calcium chloride 
(CaCl 2 ) or another hygroscopic salt main- 
tains the moisture content at the desired 
level. 



SUMMARY 



Outby dust sources at a longwall face 
can contribute significantly to face 
workers' dust exposure. They include the 
stageloader-crusher, the panel belt, and 
the intake roadways. By using recom- 
mended dust control practices, the dust 
at these sources can be adequately con- 
trolled. Sometimes several controls must 
be utilized as a system to control dust 
from many sources. 

The most effective method for elimi- 
nating the exposure of face workers to 
all outby dust sources is homotropal ven- 
tilation (tailgate-to-headgate), which 
places all outby sources downwind of the 
face workers. However, an auxilliary air 
split must be maintained for the head- 
gate operator, downwind of the mining 



activity, and the tailgate entries must 
be kept in good condition to ensure that 
intake air reaches the face. 

If homotropal ventilation is too dif- 
ficult or expensive to implement, other 
effective dust controls can be used on 
the outby sources. Stageloader-crusher 
dust controls include adding water sprays 
or utilizing a scrubber to clean the air 
inside an enclosed stageloader-crusher. 
Practices to control panel belt dust are 
proper belt entry ventilation, water ap- 
plication, belt maintenance, and belt 
cleaning. Control of intake roadway dust 
involves reducing the amount of activity 
in the roadway during the production 
shift or wetting the roadway to allay 

dust * 10287 102 



REFERENCES 



1. Jankowski, R. A., and J. A. 
Organiscak. Dust Sources and Controls on 
the Six U.S. Longwall Faces Having the 
Most Difficulty Complying With Dust Stan- 
dards. BuMines IC 8957, 1983, 20 pp. 

2. . Longwall Ventilation From 

Tailgate-to-Headgate Reduces Intake Dust. 
Technol. News, No. 145, 1982. 

3. Foster-Miller, Inc. Evaluate Fun- 
damental Approach to Longwall Dust 
Control. Ongoing BuMines contract 
J0318097; for inf., contact R. A. 
Jankowski, TPO, Pittsburgh Res. Center, 
BuMines, Pittsburgh, PA. 

4. Grigal, D. , G. Ufken, J. Sandstedt, 
M. Blom, and D. Johnson. Development of 
Improved Scrubbers for Coal Mine Applica- 
tions (contract HO199055). BuMines OFR 
91-83, 1982, 124 pp.; NTIS PB 83-205385. 



5. Goddard, B., K. Bower, and 
D. Mitchell. Control of Harmful Dust in 
Coal Mines. National Coal Board, United 
Kingdom, 1973, 85 pp. 

6. Pimentel, R. A., R. F. J. Adam, and 
R. A. Jankowski. Improving Dust Control 
on Longwall Shearers. Soc. Min. Eng. 
AIME preprint 84-113, 1984, 8 pp. 

7. Bituminous Coal Research, Inc. 
Guidebook for Dust Control in Under- 
ground Mining (contract JO199046). Bu- 
mines OFR 145-82, 1981, 206 pp; NTIS PB 
83-109207. 

8. Courtney, W. G. Single Spray Re- 
duces Dust 90 pet. Coal Min. & Proc- 
ess., v. 20, No. 6, 1983, pp. 75-77. 






* U.S. GOVERNMENT PRINTING OFFICE: 1986—605-017/40,093 



INT.-BUJ3F MINES,PGH.,PA . 28368 



U.S. Department of the Interior 
Bureau of Mines— Prod, and Distr. 
Cochrans Mill Road 
P.O. Box 18070 
Pittsburgh. Pa. 15236 



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